Nasa accepts Spirit Mars rover 'stuck for good'

The US space agency (Nasa) has admitted defeat in its battle to free the Spirit rover from its Martian sand trap.

The vehicle became stuck in soft soil back in May last year and all the efforts to extricate it have failed.

Nasa says Spirit, which landed on the Red Planet just over six years ago, will now live out its remaining days as a static science station.

The robot geologist has taken thousands of images and found evidence in Mars' rocks of a wetter, warmer past.

"Spirit has encountered a golfer's worst nightmare - the sand trap that no matter how many strokes you take, you can't get out of it," said Doug McCuistion, director of the Mars exploration programme at Nasa headquarters in Washington DC.

"But this is not a day to mourn Spirit; this is not a day of loss at this point. Spirit will continue to make contributions to science."

Like a 'polar bear'

The robot's predicament has been exacerbated by the failure of two of its six wheels. Without the additional traction, the agency now accepts that further efforts to try to escape the soft soil will be fruitless.

Instead, the mission team is concentrating on trying to get the rover tilted in a manner that will maximise the amount of sunlight falling on its solar panels during the approaching winter months. Engineers have a plan to rock the vehicle back and forth to acquire a more favourable posture.

Even so, it is likely Spirit will maintain so little energy in its batteries that it will go into hibernation, perhaps as soon as April. It will not emerge from that state until August or September, when the Sun gets high enough in the Martian sky to power up the rover's systems.

"The rover will be like a polar bear, hibernating; and it could be for many months - of the order of six months," explained John Callas, Spirit's project manager at Nasa's Jet Propulsion Laboratory.

"We have to be prepared to go through a period where we are not hearing from the rover for an extended length of time."

Far from being downbeat, Professor Steve Squyres, the rover's principal investigator, expressed some excitement at the scientific possibilities of a static vehicle.

He said the signal from a stationary Spirit could be tracked very accurately, to measure how much Mars wobbles on its axis. This could establish definitively whether the planet had a solid or a liquid core - information that scientists could use to better understand the planet's magnetic history.

This was, he said, "totally new science, never been done before - really fundamental stuff".

"This is something that I didn't really think very much about when we put a rover on the surface of Mars because we were thinking about the geology on the surface. But when you delve deeply into what this vehicle is capable of, you find new tricks; and it's something we're really excited about."

Watery past

Spirit was one of two rovers that Nasa landed on the planet in the January of 2004. The second vehicle, Opportunity, continues to roll freely on the surface.

Spirit was targeted at the 170km-wide Gusev Crater, a near-equatorial location in the southern hemisphere that orbital images had suggested might once have held a giant lake.

The investigation of this watery history got off to a slow start. Spirit initially found rocks that had undergone very limited alteration by exposure to moisture.

It was only after a 2.5km drive to nearby hills that the instrumented robot discovered rocks and soils that had experienced extensive exposure to water.

Nasa has spent more than $900m (£560m) on its Mars Exploration Rover programme, from design through to current operations. At the moment, the agency is spending about $20m a year.

The data acquired by the vehicles has generated about 100 scholarly papers, including special editions of the leading international journals Science and Nature.

Spirit became embedded in the area the mission team calls "Troy"

Nasa's Kepler planet-hunter detects five worlds

Nasa's Kepler Space Telescope has detected its first five exoplanets, or planets beyond our Solar System.

The observatory, which was launched last year to find other Earths, made the discoveries in its first few weeks of science operations.

Although the new worlds are all bigger than our Neptune, the US space agency says the haul shows the telescope is working well and is very sensitive.

The exoplanets have been given the names Kepler 4b, 5b, 6b, 7b and 8b.

They were announced at an American Astronomical Society meeting in Washington DC.

The planets range in size from an object that has a radius four times that of Earth, to worlds much bigger than even our Jupiter.

And they all circle very close to their parent stars, following orbits that range from about 3.2 to 4.9 days.

This proximity and the fact that the host stars are themselves much hotter than our Sun means Kepler's new exoplanets experience an intense roasting.

Intriguing density

Estimated temperatures go from about 1,200C to 1,650C (2,200F to 3,000F).

"The planets we found are all hotter than molten lava; they all simply glow with their temperatures," said Bill Borucki, Kepler's lead scientist from Nasa's Ames Research Center in Moffett Field, California.

THE KEPLER SPACE TELESCOPE Will study more than 100,000 suns Continuously for 4 to 6+ years Tuned to see Earth-size planets Will target the habitable zone Will also see Mars to Jupiter sizes

"In fact the upper two are hotter than molten iron and looking at them might be like looking at a blast furnace. They are very bright in their own right and certainly no place to look for life."

Kepler 7b will intrigue many scientists. It is one of the lowest-density exoplanets (about 0.17 grams per cubic centimetre) yet discovered.

"The average density of this planet with its core is about the same as Styrofoam," explained Dr Borucki. "So it's an amazingly light planet, something I'm sure theoreticians will be delighted to look at in terms of trying to understand [its] structure."

Kepler blasted into space atop a Delta II rocket from Cape Canaveral Air Force Station on 6 March, 2009.

It is equipped with the largest camera ever launched into space. The telescope's mission is to continuously and simultaneously observe more than 100,000 stars.

It senses the presence of planets by looking for a tiny "shadowing" effect when one of them passes in front of its parent star.

'Water worlds'

Kepler's detectors, built by UK firm e2v, have extraordinary sensitivity.

Nasa says that if the observatory were to look down at a small town on Earth at night from space, it would be able to detect the dimming of a porch light as somebody passed in front of it.

Artist's impression: Four of the five are bigger than a Jupiter

The space agency hopes this sensitivity will lead it to planets that are not only Earth-size but which orbit their stars at distances more favourable to life, where liquid water might potentially reside on their surfaces.

The mission's scientists told the AAS meeting that Kepler had measured hundreds of possible planet signatures but that these needed further investigation to establish their true nature.

To confirm the existence of the most ideal Earth-like planets would take a few years, they warned.

In the meantime, all detections will help scientists improve their statistics on the distributions of planet size and orbital period.

The follow-up observations needed to confirm the new exoplanets' existence used a suite of ground-based facilities including the Keck I telescope in Hawaii.